This invention relates to a heat-resistant, lubricative resin composition and a heat-resistant sliding bearing which can be used as sliding members of a heating/fixing unit in an electrophotographic device.
Sliding bearings of synthetic resin are now used in broader fields of art than before. It is required that such sliding bearings have high heat resistance so that they can exhibit good friction/wear properties especially at elevated temperatures. Such heat-resistant bearings are used e.g. in heating/fixing units for copying machines and laser beam printers.
Today, many of mating members of these bearings are made of a lightweight and soft material such as aluminum alloy. Thus, it is required to use bearings that will never damage even such soft mating members.
We will now describe how sliding bearings are used in heating/fixing units of copiers and laser beam printers.
Copiers and laser beam printers for transferring data on original images to recording material or transfer material in the form of charged images are also called electrophotographic devices. FIG. 3 shows a heating/fixing unit of such a device. It has a heating roller 10 for heating and fixing toner images on a transfer material, and a press roller 11 for rotating the transfer material by pressing it against the heating roller 10.
The heating roller 10 is in many cases made of an Mg-containing aluminum alloy and is heated by a heater 12 to about 150-230.degree. C. The press roller 11 is made of iron and covered with e.g. silicone rubber. It is heated to about 70-150.degree. C. by heat transfer from the heating roller 10.
FIG. 4 shows a different heating/fixing unit. It has, instead of the metallic heating roller 10, an endless annular fixing film 15 made of a heat-resistant synthetic resin and having a release coating. A ceramic heater 16 is pressed against the press roller 11 through the fixing film 15 to improve heat transfer efficiency. The press roller 11 of this unit is heated to higher temperatures than the press roller 11 of the unit shown in FIG. 3, in which the metallic heating roller 10 is used.
The rollers, which are heated to high temperatures as described above, are supported at both ends by synthetic resin sliding bearings 13 and 14 (in FIG. 3) or by sliding bearings corresponding to bearings 14 (in FIG. 4). Conventional such bearings were made of polyphenylene sulfide (hereinafter referred to as PPS) resin because of its high heat resistance. PPS resin is a thermoplastic synthetic resin having good heat resistance and mechanical strength. But it has poor self-lubricating properties, so that it is usually necessary to add graphite, tetrafluoroethylene resin, lubricating oil, metallic oxides, aromatic polyamide resin, etc. as lubricants.
For higher performance of an electrophotographic device having sliding members made of synthetic resin, more specifically, in order to increase its copying or printing speed, it is necessary to melt and fix toner as quickly as possible. For this purpose, it is essential that the sliding bearings 13 and 14 be made of a material that can withstand heating up to a temperature of 250-270.degree. C.
In this regard, the conventional sliding members made of PPS resin, having a melting point near 280.degree. C., are not sufficiently heat-resistant for the above the purpose.
Unexamined Japanese Patent Publication 63-8455 proposes to improve the sliding properties of an inherently heat-resistant polyimide resin by adding tetrafluoroethylene resin.
Unexamined Japanese Patent Publication 63-314712 proposes to add tetrafluoroethylene resin and a hardened phenolic resin to a polyimide resin to improve its wear resistance.
Such conventional sliding members made of polyimide resins exhibit good sliding properties with respect to mating members which are hard at room temperature. But if they are brought into sliding contact with mating members made of a soft metal such as aluminum or an aluminum alloy, they tend to severely damage the mating members.
It is of course impossible to prevent damage to soft aluminum alloys simply by adding carbon fiber to the compositions. When the mating members are damaged, friction/wear properties may be aggravated.
An object of this invention is to provide a heat-resistant, lubricative resin composition which can withstand temperatures of 250-270 C., which is wear-resistant and low in friction, which is less likely to attack a soft alloy such as aluminum alloy, and which have superior properties to any conventional composition formed mainly from a polyimide resin, and high-performance, heat-resistant sliding bearings formed from the abovementioned heat-resistant, lubricative resin composition.